The contamination of water by nitrate ions has become a growing problem worldwide due to the use of nitrogen fertilizers and the inadequate treatment of wastewater. The electrochemical method of catalytic reduction of nitrate offers an alternative in the detection and remediation areas of nitrate-polluted groundwaters. In this method, the electrode area formed by combination of different metals [1, 2] becomes important as it increases the reaction rate of the process. Another way could be the modification of the substrate with an adsorbed submonolayer of another metal, through the UnderPotential Deposition (UPD) phenomenon [3]. On the other hand, bimetallic nanoparticles have attracted great attention, because their properties are better than those of monometallic counterparts. These properties increase their function and application in many fields, including electrocatalysis.

In this work we compare different electrode surfaces to be used as potential catalysts: single Ag crystals, supported Ag films and nanoparticles, modified with UPD Cd deposits. The silver deposits are generated by potentiostatic pulses on a highly ordered pyrolytic graphite (HOPG) substrate. In this study, conventional electrochemical and characterization techniques (SPM, SEM, XPS) are used. The electrocatalytic effect of the nanostructured surfaces is analyzed.

The voltammetric results indicated that the formation of underpotentially deposited Cd on Ag particles follows a behavior different from that observed for single crystal Ag electrodes [4]. The behavior of the Cd UPD on a modified Ag film/HOPG substrate is similar to that obtained with massive Ag substrates, indicating that the Cd adsorption occurs on HOPG practically covered with Ag. The voltammetric results of the system Cd/Ag(NPs)/HOPG, involved only the formation of a Cd UPD monolayer on Ag (NPs), and an increase in current density prior to this process related to the presence of Cd expanded structures. The morphology images showed similar sized Ag particles distributed preferably over the step edges of the HOPG. No noticeable morphological changes were observed on the surface after the subsequent deposition of Cd, indicating the formation of Cd-Ag core-shell structures.

The modified electrodes were analyzed by cyclic voltammetry in a solution containing different concentrations of nitrate ions. A higher reduction current was verified for longer polarization times used in Cd deposition on supported Ag(NPs).